Chimeric peptide immunogens

ABSTRACT

Chimeric peptide epitopes can serve as effective immunogens against hormones and other small peptides or proteins. Thus, immunogenic peptides are selected from promiscuous Th epitopes and synthesized together with self antigenic peptide sequences fused with or without end to end spacer peptide interconnections. A peptide sequence which may be of the gonadotropin releasing hormone is linked with an immunogenic peptide sequence selected from a promiscuous Th-epitope of measles virus protein F, tetanus toxoid, or malaria protein CSP. Compositions of the chimeric immunogen are found effective in eliciting high and specific anti-GnRH antibody titers.

This application claims priority from the provisional application No. 60/202,328, filed May 5, 2000 in the United States Patent and Trademark Office.

FIELD OF THE INVENTION

The invention is related to chimeric peptides having immunogenic efficacy, comprising a hormone epitope and promiscuous helper T-cell epitope for the production of high titers of anti-hormone antibodies.

BACKGROUND OF THE INVENTION

The success of an antigenic composition is linked to its immunogenicity, that is, the ability to produce a sufficiently high titer of antibodies to react or bind with the target antigen or so as to neutralize its effects. The immunogenicity depends on the effectiveness by which the antigen causes the body's immune system to mount a response which can be generally assessed on the basis of the antibody titer in the blood of the immunized animal or mammal including the human.

Antigenic formulations can be prepared for antigens of low immunogenicity with constructs or mixtures of an immunomimic epitope of the target antigen and an immunogen not related to the target antigen so as to generate a strong immune response against the entire immunogenic construct or mixture so as to be effective against the specific target antigen.

In order to enhance or potentiate the immune defense system, so-called adjuvants in the form of oily substances and other potentiating and emulsifying agents are added to the antigenic formulations. In general, the adjuvant is mixed into the immunogenic emulsion formulation and simultaneously delivered with the antigen in the same administration, e.g., by injection. Specifically, antigenic formulations have been enhanced to target less immunogenic microorganisms or viral pathogens by the addition of so-called adjuvants comprising immune response-stimulating killed microbial cells, particles or fragments thereof. Moreover, immunogenic compositions may contain carrier components, including emulsions, liposomes, microparticles and implantable vehicles which may be metabolizable.

Immunization technology has been applied as a biological modifying means to immunize against various soluble and insoluble animal or human self-antigens, which are not normally recognized by the individual host's own immune defense, but which may be rendered immunogenic so as to stimulate or potentiate the individual's own immune response system. The self-antigens may include the surfaces of certain cells which are malfunctioning or malignant, and small proteins, enzymes or intercellular signals, such as, e.g., hormones or other factors, and/or their cognate receptors, whether normal or deficient. The lack of immunogenicity of these self-antigens has been often overcome by complexing or linking the non-immunogenic self-antigens with a pharmaceutically acceptable, i.e. non-toxic, immunogenic carrier so as to produce antibodies capable of binding, thereby neutralizing, the self-antigen of the subject animal or human patient.

The immunological methods can be used for example in the therapeutical hormone control or regulation and the treatment of patients afflicted with a disorder or disease.

Some immunogens suitable for hormone-regulation comprise hormone immunomimicking molecular moieties which are conjugated or fused to immunogenic carriers, such as, e.g., proteins, or peptides or complex polysugars. The immunogenic constructs are usually administered as either an oil-in-water or a water-in-oil emulsion, containing an adjuvant capable of stimulating or potentiating an immune response.

An immune response is typically measured in terms of the production of specific anti-hormone antibodies. The hormones and cognate receptors which are targeted for control by the immunological methods are directly neutralized or inhibited by the antigen-binding reaction of circulating hormone specific antibodies elicited by the injected immunogenic constructs.

For example, an anti-hormone immunogen has been constructed to affect the regulation of the gonadotropin releasing hormone (see co-assigned U.S. Pat. No. 5,688,506). The Gonadotropin Releasing Hormone (abbreviated “GnRH”, also known as Luteinizing Hormone Releasing Hormone, abbreviated “LHRH”), is of central importance to the regulation of fertility. Johnson M et al., Essential Reproduction, 3^(rd) Edn. Blackwell Scientific Publications (1988). In both males and females, GnRH is released from the hypothalamus into the bloodstream and is transported through the bloodstream to the pituitary, where it induces the release of gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH), by the gonadotrophs. These gonadotropins, in turn, act upon the gonads, inducing steroidogenesis and gametogenesis. Steroids released from the gonads into the circulation subsequently act upon various tissues. This gonadotropin related hormonal cascade can be halted by the neutralization of the biological activity of GnRH. Fraser H. M., Physiological Effects of Antibody to Lutenizing Hormone Releasing Hormone, Physiological Effects of Immunity Against Reproductive Hormones, Edwards and Johnson, Eds. Cambridge University Press (1976). As a consequence of GnRH neutralization, the gonadotropins and gonadal steroids are not released into the blood, and their biological activities are curtailed or eliminated by the direct and indirect action of specific anti-GnRH antibodies. By eliminating the physiological activity of GnRH, the cascade of hormonal regulation of fertility is interrupted and gametogenesis ceases. Consequently, GnRH neutralization halts the production of gametes. Thus, GnRH neutralization is an effective means of contraception.

A number of important diseases are affected by gonadotropins and particularly gonadal steroid hormones. Such diseases include breast cancer, uterine and other gynecological cancers, endometriosis, uterine fibroids, benign prostatic hypertrophy and prostate cancer, among others. Removal of the gonadal steroid hormonal stimuli for these diseases constitutes an important means of therapy. An effective method of accomplishing this is by immunologically neutralizing GnRH, to thereby eliminate or inhibit production of GnRH dependent gonadal steroids that induce and stimulate these diseases. McLachlan R. I. et al. Clinical Aspects of LHRH Analogues in Gynaecology: a Review, British Journal of Obstetrics and Gynaecology, 93:431-454 (1986); Conn P. M. et al. Gonadotropin-Releasing Hormone and Its Analogs, New England Journal of Medicine. 324:93-103 (1991) and Filicori M. GnRH Agonists and Antagonists, Current Clinical Status. Drugs. 35:63-82 (1988).

Since GnRH has the same amino acid sequence in all mammals (pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-GlyNH₂, SEQ ID NO: 1 in the Sequence Listing), it is presumed that a single immunogen would be effective in all mammalian species, including humans. An anti-GnRH immunogenic construct, comprising the GnRH immunomimic domain in the form of peptide analogues, may be linked or conjugated to a carrier protein which is effectively immunogenic, such as, e.g., diphtheria toxoid, tetanus toxoid, keyhole limpet hemocyanin, bovine serum albumin, Hemophilae pertussis extracts or filamentous Amycolata extracts. Consequently, the immune response to the GnRH-vaccine will be mostly directed against the carrier protein and secondarily, the attached hormone epitope moiety. In general, as an alternative approach, the immunogenicity of the immunomimic peptide can be enhanced by chemical modification with diazosulfuric acid groups.

Various anti-GnRH immunogenic compositions have been useful for producing specific anti-GnRH antibodies. Immunogenic conjugates of GnRH-immunomimic epitope peptide and immunogenic protein carriers have been used for immunization of vertebrate subjects against the hormone, GnRH (U.S. Pat. No. 5,688,506).

As another example, anti-hormone immunogens have been constructed to affect or inhibit the activity of the stomach hormone gastrin, in particular, the major forms of gastrin, gastrin G17 and gastrin G34 (see U.S. Pat. Nos. 5,023,077, and 5,468,494). It has been found that especially G17 is involved in gastrointestinal disorders and diseases such as gastroesophageal reflux disease, gastric and duodenal ulceration and cancer.

However, it has been found that perhaps due to the comparatively huge size of the attached immunogenic carrier proteins, the immunization of the conjugate can induce anti-epitope specific suppression of the antibody (Sad et al. Immunology, 1985, 74:559; Schutze et al. J. Immunol, 1985, 135:231). Therefore, much smaller immunogenic proteins have been tried. Accordingly, short synthetic T-helper epitopes have been introduced to replace the large carrier molecules in conjugates to improve the efficacy of the anti-hormone or self antigenic immunogen. Sad et al. (Vaccine 1993, 11:1145-1149) synthesized peptides from DT and universal or highly promiscuous T-helper epitopes from TT (829-844 amino acids, SEQ ID NO: 2) or CSP (378-398 aa; SEQ ID NO: 3) in order to try to minimize genetic restriction of the immune response. To be effective, the GnRH vaccines of Sad et al. required Freund's Complete Adjuvant.

Gosh et al. (Int. Immunology, 1999, 11:1103-1110) reported that some synthetic LHRH (GnRH) chimeric vaccines elicited an immune response for sterilization of mice. However, the promiscuous helper T-cell (Th)-epitope candidate T1 (TT sequence 947-967 aa, SEQ ID NO: 4) was not regarded promiscuous enough to be applicable for a large number of animal species. It was also reported that in a shift, antisera from second bleedings reacted significantly with the anti-Th epitope (T2) and much less with the LHRH antigen.

SUMMARY OF THE INVENTION

The present invention provides immunogens comprising a chimeric peptide of a hormone-immunomimic peptide epitope fused in sequence with an immunogenic epitope. The hormone immunogenic peptide can be fused either directly to or through a spacer sequence to an immunogenic peptide epitope.

These fusion peptides combine at least one epitope of a target substance which may be non immunogen in its natural state with at least one immunogenic peptide sequence of suitable immunogenic proteins. The sequences of both target epitope and immunogen may be selected from the amino-terminal or carboxy-terminal region or both. A peptide also can be synthesized from the internal region of the peptide or protein. The fusion product may be acetylated at the amino-terminal end and amidated at the carboxy-terminal end of the peptide sequence. An embodiment of the invention provides a synthetic immunogenic fusion peptide selected from the group consisting of one or more than one peptide defined by SEQ ID NO: 10 and SEQ ID NO: 11.

An embodiment of the invention provides an anti-GnRH immunogen chimeric peptide construct comprising a suitable immunogenic epitope, such as, e.g., short peptide sequences selected from the measles virus protein F (MVF), tetanus toxoid (TT), or malaria plasmodium falciparum CSP protein. The invention also provides for methods of immunization with a composition comprising a chimeric peptide with one or more GnRH epitopes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the mean Anti-GnRH antibody titers obtained from rabbits using chimeric anti-GnRH Immunogens A through J, and as controls, Immunogens K and L as well as conjugate immunogen C, GnRH:DT; and

FIG. 2 illustrates the relationship between gross muscle reaction score and mean anti-GnRH Antibody Titer on GnRH Chimeras and Controls.

DETAILED DESCRIPTION OF THE INVENTION

Chimeric peptides comprising GnRH mimicking epitopes have been constructed and useful in generating improved antibody titers.

Since self-antigen epitopes of gonadotropin releasing hormone (GnRH) are not inherently immunogenic the immune response may be aided by immunogenic constructs according to the invention wherein a target peptide epitope is located on the same synthesized peptide as is an immunogenic peptide epitope.

Several different chimeric peptides are described in Example 1.

EXAMPLE I

The peptide sequences combine a select promiscuous T-helper-epitope through an inserted short spacer peptide (e.g., 4-8 amino acids) with at least one target hormone peptide. Suitable spacers of this invention include but are not limited to the peptides comprising the following amino acid sequence, GPSL (see SEQ ID NO: 5); SSGPSL (SEQ ID NO: 6); and SSGPSLKL (SEQ ID NO: 7), which are inserted in the peptide chimera to isolate the three dimensional folding of the immunogenic peptide from that of the hormone peptide.

Promiscuous Th-epitope moieties from measles virus protein F (MSF) (sequence 288-302 aa, SEQ ID NO: 8), tetanus toxoid (TT) (sequence 947-967 aa, SEQ ID NO: 4, or sequence 830-844 aa, SEQ ID NO: 2) and malaria Plasmodium falciparum CSP protein (sequence 378-398 aa, SEQ ID NO: 3) are used in these constructs. The hormone immunomimic epitopes were attached to the N-terminal or the C-terminus of the spacer as shown below. All mammalian GnRH peptides including the human hormone, have the same sequence. The GnRH hormone immunomimic epitope sequence comprises 1-10 amino acids of mammalian GnRH when attached to the aminoterminal peptide end and comprises 2-10 amino acids of mammalian GnRH when attached to the carboxyterminal peptide end. In addition, an immunomimic peptide comprising 13-16 amino acids of the mammalian GnRH comprise GnRH immunomimics peptides attached to both ends of the spacer, in order to increase the number of available GnRH antigenic epitopes. The different peptide chimera fusion immunogens in terms of antibodies produced are described below.

Peptide 1.

Peptide 2.

Peptide 3.

Peptide 4.

Peptide 5.

Peptide 6.

Peptide 7.

Peptide 8.

Peptide 9.

Peptide 10.

Peptide 11.

Peptide 12.

EXAMPLE II

Immunogenicity tests were performed with five chimeric peptide immunogens against GnRH. Each chimeric peptide contained one region encoding an epitope to be recognized by helper T-cell and a second region encoding an immunomimic of GnRH, to serve as the target for the antibody response. The chimeric peptide immunogens were formulated to deliver 100, 250 or 500 μg doses of peptide with 3 μg norMDP, in a water in oil emulsion. Control immunogens were prepared to deliver 500 μg of mammalian GnRH (1-10) Ser1 peptide (which is normally linked to an immunogenic carrier to impart immunogenicity), with and without norMDP (3 μg), in the same emulsions. The immunogens were given intramuscularly to rabbits in three injections, on days 0, 14 and 42. An ELISA procedure was used to measure the resultant anti-GnRH antibody responses in sera collected at 14-day intervals over the course of the immunization. Injection site reactions were assessed by visual and microscopic evaluations on day 84.

The following materials were used in the immunogenicity tests. The five immunogens of GnRH chimera peptides tested were selected from the aforementioned Peptide 1 through 16.

-   -   1. GnRH chimera 1 {MVF (Measles Virus Protein F)} “Peptide 1”         (MW 3427.17)     -   2. GnRH chimera 2 {TT-3 (Tetanus Toxoid Epitope 3)} “Peptide 2”         (MW 3886.52)     -   3. GnRH chimera 3 {TT-2 (Tetanus Toxoid Epitope 2)} “Peptide 3”         (MW 3132.6)     -   4. GnRH chimera 4 {MCSP (Malaria Circumsporozoite Protein)}         “Peptide 4” (MW 3632.2)     -   5. GnRH chimera 6 (TT-3, N-ter GnRH) “Peptide 6” (MW 4172.7)     -   6. D17 Peptide (“GnRH (1-10) Ser 1”)

For testing the GnRH chimeric peptide immunogens were formulated at concentrations listed below in Table 1. Each injection volume was 0.2 ml/dose (see Table 2). TABLE 1 GnRH Chimera and Control Immunogen Formulations Concentration Concentration of Peptide in Peptide of norMDP in norMDP Chimeric Emulsion Dose Emulsion Dose Immunogen Peptide (mg/ml) (μg/dose) (mg/ml) (μg/dose) A Peptide 1 2.5 500 0.015 3 B Peptide 2 2.5 500 0.015 3 C Peptide 2 1.25 250 0.015 3 D Peptide 2 0.5 100 0.015 3 E Peptide 3 1.25 500 7.2 × 10⁻³ 3 F Peptide 4 2.5 500 0.015 3 G Peptide 6 2.5 500 0.015 3 H Peptide 2 2.5 500 0.015 3 I Peptide 3 1.25 500 7.2 × 10⁻³ 3 J Peptide 2 & 3 0.625, each 250, each 7.2 × 10⁻³ 3 peptide peptide K D17 Peptide 2.5 500 0.015 3 L D17 peptide 2.5 500 — —

The GnRH chimeric immunogenic compositions and control immunogens were formulated under clean conditions in the combinations shown in Table 1. The test materials were sterile bottled and stored under refrigeration (2-8° C.).

New Zealand White female rabbits were immunized with GnRH chimera and control immunogens as shown in Table 2. Injections were given to each rabbit on days 0, 14 and 42 in dose volumes of either 0.2 ml or 0.4 ml. All immunogens were given IM, at injection sites tattooed for later identification.

To assess immunogenicity, sera were obtained from each rabbit every 14 days until day 84. Anti-GnRH antibody titers were measured in the sera samples by a direct binding ELISA. All values, with the exception of those for immunogen 6, are expressed relative to a reference standard rabbit anti-GnRH serum reference titer of 5,000. Titers of sera against Immunogen 6 (Peptide 6 N-terminal specific antibodies) were expressed relative to the reference standard rabbit anti-GnRH serum Ser 10(11) reference titer of 20,000.

Although the original study had two rabbit groups, the protocol was later amended to add two more groups (n=4), 3 and 4, with amounts of 250 μg and 100 μg of GnRH chimera 2 (TT-3) (Peptide 2), each with 3 μg of norMDP. TABLE 2 Example II: Immunization Schedule Rabbit Injection Group Volume Number N* Peptide(s) (ml/dose) 1 4 Peptide 1 500 μg 0.2 2 4 Peptide 2 500 μg 0.2 3 4 Peptide 2 250 μg 0.2 4 4 Peptide 2 100 μg 0.2 5 4 Peptide 3 500 μg (2 × 0.2/ site)** 6 4 Peptide 4 500 μg 0.2 7 4 Peptide 6 500 μg 0.2 8 10 Peptide 2 500 μg 0.2 9 10 Peptide 3 500 μg (2 × 0.2/ site)** 10 6 Peptides 2 & 3, 250 μg (2 × 0.2/ each site)** 11 4 D17 peptide (500 μg) with 0.2 norMDP 12 4 D17 peptide 500 μg 0.2 *N = number of rabbits per group **Peptide 3 did not dissolve at higher concentrations, therefore injection volumes were doubled to deliver 500 μg/dose of total peptide.

Since GnRH chimera peptide 3 (“Peptide 3”) (TT-2) was not found soluble at 9.412 mg/ml in aqueous phase, the original protocol was amended to reduce the concentration in half (4.706 mg/ml) and double the dose volume to maintain 0.2 ml volume per injection (2×0.2 ml/site). Injection #3 was delivered on day 42. Titers obtained for the individual serum samples are given in Table 3A/B/C, and mean titers for all groups are plotted in FIG. 1, respectively. In the initial tests, all rabbits responded to the chimera peptides with the production of anti-GnRH antibody titers. Peptide 3 or GnRH chimera 3 (TT-2) induced significantly higher antibody titers in comparison with the other chimera peptides. Peptide 2 or Chimera 2 was most immunogenic at the 500 μg dose (Immunogen B), with the 100 μg (Immunogen D) and 250 μg (Immunogen C) doses inducing weaker titers. Chimeras 2 (Immunogen B) and 3 (Immunogen E) induced high antibody titers in the initial tests (n=4) relative to titers induced by GnRH:DT; however, these titers were lower in the repeat studies (n=10, Immunogen H where the response rate was quite variable, and Immunogen I, respectively).

A combination of Chimeras 2 and 3 (Immunogen J), at 250 μg dose of each (half the dose used in rabbits injected with the individual peptides) induced high titers of anti-GnRH antibody. Chimeras 1 (Immunogen A), 4 (Immunogen F) and 6 (Immunogen G) were not as potent as the GnRH:DT conjugate formulated in Montanide ISA 703 (as historical control included in FIGS. 1 and 2). It should be noted that Peptide 6 or GnRH chimera 6 (TT-3 in aminoterminal position) titers were measured using an N-terminus specific reference standard, therefore a statistical comparison of these titers with other chimera peptides was not performed. Nevertheless, Peptide 6 was concluded not to be an effective immunogen. Very low anti-GnRH antibody titers were induced by D17 peptide adjuvanted with norMDP (Immunogen K), while without norMDP (Immunogen L), the D17 peptide emulsion was not immunogenic.

Gross pathology of injection sites was assessed on all rabbits on day 84. The evaluation was scored on a scale of 0-3, where a score of 0 indicated normal tissue appearance and 3 indicated the presence of extensive tissue inflammation. Scores of 1 or 2 were judged intermediate levels of local reaction. TABLE 3A Example II: Anti-GnRH Antibody Titers for GnRH Chimeras Injection Injection 2 Injection 3 Injection 1 (Day 14) (Day 42) (Day 0) Day Day Day Day Day Day Immunogen Rabbit # Day 0 14 28 42 56 70 84 A  1 0 274 3,276 8,845 12,500 20,600 13,200  2 0 0 636 2,193 4,667 13,400 8,249  3 0 0 198 512 731 1,392 1,166  4 0 0 0 0 0 0 0 Mean 0 69 1,028 2,888 4,475 8,848 5,654 Median 0 0 417 1,353 2,699 7,396 4,708 S.D. 0 137 1,522 4,081 5,729 9,878 6,213 B  5 0 8,201 20,500 37,400 34,500 62,100 76,800  6 0 12,400 46,400 81,200 134,000 93,100 108,000  7 0 507 22,300 91,800 75,000 50,600 28,400  8 0 589 2,085 16,100 24,800 31,800 32,700 Mean 0 5,424 22,821 56,625 67,075 59,400 61,475 Median 0 4,395 21,400 59,300 54,750 56,350 54,750 S.D. 0 5,886 18,181 35,838 49,632 25,705 37,953 C  9 0 0 536 1,325 6,631 7,267 5,033 10 0 0 1,240 3,551 19,700 19,600 7,886 11 0 0 719 16,800 12,800 16,800 11,200 12 0 0 454 2,671 5,017 5,844 3,692 Mean 0 0 737 6,087 11,037 12,378 6,953 Median 0 0 628 3,111 9,716 12,034 6,460 S.D. 0 0 353 7,201 6,679 6,844 3,328 D 13 0 2,952 8,320 869 87,200 47,300 39,700 14 0 841 21,600 57,500 93,000 25,100 11,800 15 0 141 1,759 4,373 7,732 6,670 5,198 16 0 0 5,220 7,044 7,363 6,120 4,731 Mean 0 984 9,225 17,447 48,824 21,298 15,357 Median 0 491 6,770 5,709 47,466 15,885 8,499 S.D. 0 1,363 8,674 26,822 47,721 19,450 16,546 E 17 0 1,382 15,500 140,000 79,900 136,000 105,000 18 0 264 13,200 50,800 41,700 120,000 145,000 19 0 471 13,000 98,900 95,700 111,000 131,000 20 0 2,317 13,400 35,900 52,800 80,500 85,100 Mean 0 1,109 13,775 81,400 67,525 111,875 116,525 Median 0 927 13,300 74,850 66,350 115,500 118,000 S.D. 0 941 1,162 47,423 24,703 23,332 26,713 F 21 0 296 3,189 2,638 2,165 2,751 3,365 22 0 0 441 5,920 4,912 8,760 12,200 23 0 0 484 6,350 6,333 7,900 7,512 24 0 0 3,556 60,300 20,400 24,300 18,700 Mean 0 74 1,918 18,802 8,453 10,928 10,444 Median 0 0 1,837 6,135 5,623 8,330 9,856 S.D. 0 148 1,687 27,716 8,151 9,301 6,582

TABLE 3B Example II: Anit-GnRH Antibody Titers for GnRH Chimeras continued) Injection Injection 2 Injection 3 Injection 1 (Day 14) (Day 42) (Day 0) Day Day Day Day Day Day Immunogen Rabbit # Day 0 14 28 42 56 70 84 G 25 0 0 0 0 105 640 1,165 26 0 0 0 0 0 131 141 27 0 0 0 166 914 3,554 3,830 28 0 0 0 191 387 1,265 1,510 Mean 0 0 0 89 352 1,398 1,662 Median 0 0 0 83 246 953 1,338 S.D. 0 0 0 104 409 1,511 1,558 H 29 0 0 0 0 208 708 693 30 0 0 1,257 1,475 2,800 2,374 2,313 31 0 0 0 0 0 0 0 32 0 0 0 147 1,319 2,051 1,559 33 0 204 3,713 8,696 11,900 14,100 11,200 34 0 0 413 480 ** 16,900 14,700 35 0 0 366 326 1,879 3,462 3,022 36 0 0 0 0 200 410 555 37 0 0 163 774 2,825 4,677 5,109 38 0 2,787 8,027 7,742 41,700 63,200 62,900 Mean 0 299 1,394 1,964 6,981 10,788 10,205 Median 0 0 265 403 1,879 2,918 2,668 S.D. 0 877 2,597 3,335 13,523 19,319 19,149 I 39 0 0 228 877 7,841 12,200 9,998 40 0 0 2,568 5,522 27,000 29,600 17,000 41 0 895 7,474 31,400 29,500 46,300 34,500 42 0 0 1,560 3,280 10,800 12,000 11,500 43 0 222 3,510 16,600 20,600 31,300 26,500 44 0 0 5,825 22,500 27,000 36,200 37,900 45 0 1,249 24,300 39,300 65,000 67,700 69,100 46 0 498 5,208 7,243 8,877 13,500 16,800 47 0 0 2,091 5,509 10,100 19,200 18,300 48 0 0 4,072 7,937 14,600 26,300 48,400 Mean 0 286 5,684 14,017 22,132 29,430 29,000 Median 0 0 3,791 7,590 17,600 27,950 22,400 S.D. 0 452 6,886 13,061 17,164 17,535 18,782 J 49 0 219 4,179 33,900 81,500 85,300 113,000 50 0 8,659 100,000 193,000 242,000 169,000 129,000 51 0 305 14,800 89,500 91,300 97,800 69,000 52 0 1,071 11,000 26,600 30,600 27,500 19,300 53 0 554 16,300 64,000 32,500 31,400 31,100 54 0 1,940 32,700 86,400 70,500 65,600 68,800 Mean 0 2,125 29,830 82,333 91,400 79,433 71,700 Median 0 813 15,550 75,200 76,000 75,450 68,900 S.D. 0 3,263 35,647 60,172 77,950 52,134 43,356 K C1 0 746 1,515 2,201 1,918 2,074 1,913 C2 0 0 0 0 0 0 0 C3 0 134 590 953 998 1,238 1,768 C4 0 323 2,279 1,345 1,225 1,640 987 Mean 0 301 1,096 1,125 1,035 1,238 1,167 Median 0 229 1,053 1,149 1,112 1,439 1,378 S.D. 0 325 1,005 913 793 893 878 L C5 0 0 0 0 0 0 0 C6 0 0 0 0 0 0 0 C7 0 0 0 0 107 0 0 C8 0 0 0 0 0 0 0 Mean 0 0 0 0 27 0 0 Median 0 0 0 0 0 0 0 S.D. 0 0 0 0 54 0 0

TABLE 3C Example II: Anit-GnRH Antibody Titers for GnRH Chimeras Injection Injection 2 Injection 3 (Day (Day Injection 1 14) 42) (Day 0) Day Day Day Day Day Day Immunogen Rabbit # Day 0 14 28 42 56 70 84 Control C9  0 475 7,210 11,400 8,812 8,762 8,338 GnRHDT Conjugate in C10 0 1,588 9,253 20,100 28,500 34,800 32,200 Emulsion = 0.5 mg/ml C11 0 0 4,593 17,700 25,100 35,400 19,800 Conjugate Dose = 100 μg C12 0 194 3,647 7,900 13,900 12,900 11,800 Dose Volume = 0.2 ml C13 0 169 1,565 2,559 4,752 7,204 7,115 C14 0 651 3,965 3,755 8,277 13,700 7,179 C15 0 123 2,785 2,627 4,198 5,218 3,891 C16 0 353 4,910 13,800 26,700 43,600 30,600 C17 0 333 8,573 25,100 30,300 57,400 26,200 C18 0 188 2,171 2,622 7,314 8,207 8,404 Mean, 0 407 4,867 10,756 15,785 22,719 15,553 Group 5 Median, 0 264 4,279 9,650 11,356 13,300 10,102 Group 5 S.D. 0 455 2,653 8,216 10,617 18,486 10,695 * test titers are read at 20,000 titer of the reference standard, lot 122298SHG2

The score data are summarized in Table 4, indicating that most of the visual injection site scores ranged from 0 to 1, indicating that the immunogens were generally well tolerated. Histologic readings of the injection site biopsies which were performed as of day 84 were in accord with the gross evaluation.

These experiments demonstrated that chimera peptides carrying a T-lymphocyte epitope and expressing an immunomimic of GnRH can be used to induce potent anti-GnRH antibody responses. Peptides bearing TT-2 and TT-3 T-lymphocyte epitopes, derived from TT, were more effective than the T-lymphocyte epitopes derived from MVF and MCSP. A combination of the TT-2 and TT-3 bearing chimeras was particularly effective. It was surprisingly found that the GnRH epitope had to be on the carboxyterminus of the chimeras to be immunogenic. Most injection site reactions were of an acceptable level. Overall, the response compared favorably with those induced by the GnRH:DT (previously named, D17-DT) conjugate, indicating that the synthetic peptides could potentially enhance the choice of effective immunogens and perhaps even replace the conjugate method for producing an active component of the GnRH immunogen. TABLE 4 Example II: Reaction Scores MEAN REACTION SCORES REACTION SCORES > 1 Injection 1 Injection 2 Injection 3 Injection 1 Injection 2 Injection 3 Immunogen SITE 1 SITE 2 SITE 1 SITE 2 SITE 1 SITE 2 SITE 1 SITE 2 SITE 1 SITE 2 SITE 1 SITE 2 A 0 0.5 0.5 0 0 0 B 0.4 1.1 1.1 0 1 1 C 0.1 0.5 0.5 0 0 0 D 0.3 0.4 1.0 0 0 1 E 0.6 0.3 0.9 0.6 0.8 1.3 0 0 1 0 0 1 F 0.5 1.1 1.1 0 1 1 G 0.1 0.3 0.8 0 0 0 H 0.1 0.3 0.4 0 0 0 I 0 0.4 0.1 0.5 0.6 0.7 0 0 0 0 1 1 J 0 0.4 0.5 0.5 1.0 1.3 0 0 0 0 1 2 K 0.4 0.4 1.0 0 0 1 L 0.3 0 0.3 0 0 0 Conjugate Ctl. 0.4 0.6 0.9 0 0 1 

1-16. (canceled)
 17. A method of producing an anti-GnRH immune response-inducing synthetic immunogen, the method comprising fusing (i) a promiscuous helper T-lymphocyte epitope selected from the group consisting of SEQ ID NO: 8 of measles virus protein F (MVP-F), SEQ ID NO: 2 of tetanus toxoid (TT), SEQ ID NO: 4 of tetanus toxoid (TT), and SEQ ID NO: 3 of malaria circumsporozoite protein (M-CSP); through (ii) a spacer peptide selected from the group consisting of Gly-Pro-Ser-Leu (SEQ ID NO: 5), Ser-Ser-Gly-Pro-Ser-Leu (SEQ ID NO: 6), and Ser-Ser-Gly-Pro-Ser-Leu-Lys-Leu (SEQ ID NO: 7) to (iii) a GnRH immunomimic peptide comprising either the amino acid sequence of SEQ ID NO: 1, or amino acids 2-10 of SEQ ID NO:
 1. 18. The method according to claim 17, comprising fusing the T-lymphocyte epitope through the spacer peptide to the amino-terminus or the carboxy-terminus of the GnRH-immunomimic peptide.
 19. The method according to claim 18, further comprising fusing a second GnRH immunomimic peptide comprising either the amino acid sequence of SEQ ID NO: 1, or amino acids 2-10 of SEQ ID NO: 1, through a spacer peptide to the T-lymphocyte epitope; wherein the second GnRH immunomimic peptide is fused at its carboxy-terminus or its amino-terminus.
 20. The method according to claim 17, wherein the T-lymphocyte epitope is fused through a spacer peptide to the amino-terminus of the GnRH-immunomimic peptide.
 21. The method according to claim 17, wherein the synthetic immunogen comprises a GnRH-immunomimic peptide having an acetylated amino-terminal glutamic acid or an amidated carboxy-terminal glycine.
 22. A method of producing an anti-GnRH immune response-inducing synthetic immunogen, the method comprising fusing a promiscuous helper T-lymphocyte epitope through a spacer peptide to a GnRH immunomimic peptide selected from the group consisting of the peptide defined by SEQ ID NO: 9, SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, and SEQ ID NO:
 20. 23. The method according to claim 22, wherein the synthetic immunogen is the peptide defined by SEQ ID NO: 10 or SEQ ID NO:
 11. 24. A method of producing an anti-GnRH immune response-inducing synthetic immunogen, the method comprising combining at least two different fusion peptides selected from the group consisting of the peptide defined by SEQ ID NO: 9, SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, and SEQ ID NO:
 20. 25. The method according to claim 24, wherein the combination of synthetic immunogen comprises: (i) the synthetic immunogen defined by SEQ ID NO: 10; and (ii) the synthetic immunogen defined by SEQ ID NO:
 11. 